With respect to wiring boards, for example, for mounting on a vehicle, there have been extensively used the type of wiring boards in which a connector is connected to a side edge portion of the wiring board, and the wiring board is connected to a wire harness through this connector (see, for example, PTL 1). FIG. 6 is a perspective view showing a connector connecting structure of a related wiring board, FIG. 7A is a plan view thereof, FIG. 7B is a front-elevational view thereof (a cross-sectional view taken along the line B-B′), and FIG. 7C is a side-elevational view thereof. As shown in FIG. 7A, a large-current circuit pattern 102a and a small-current circuit pattern 102b are formed on a face of the wiring board 101. In the wiring board 101, left and right areas (in the drawings) serve as terminal connecting areas 101a, respectively, and a central area serves as a parts-mounting area 101b. 
A plurality of through holes 103 (103a to 103c) are formed through the terminal connecting area 101a, and are arranged in three rows. L-shaped terminals 104 (104a to 104c) are connected to the through holes 103, respectively. In this case, as shown in FIG. 7B, the L-shaped terminal 104c connected respectively to the through holes 103c disposed in the first row counting from an end of the wiring board are bent perpendicularly (that is, at right angles) at a height h1, and the L-shaped terminals 104b connected respectively to the through holes 103b disposed in the second row are bent perpendicularly at a height h2 (>h1), and the L-shaped terminals 104a connected respectively to the through holes 103a disposed in the third row are bent perpendicularly at a height h3 (>h2).
As shown in FIG. 7C, through holes 106 (106a to 106c) of a three-tier structure arranged in first, second and third tiers are formed through an end wall of a connector 105, and the L-shaped terminals 104a to 104c extend respectively through the corresponding through holes 106a to 106c and project into the interior of the connector 105. The connector 105 is fixed to the wiring board 101. Therefore, the wiring board can be connected to a wire harness (not shown), using the connector 105.
The through holes 103a disposed in the third row are used for a large-current circuit, and the large-current circuit patterns 102a are connected to these through holes 103a. The through holes 103c and 103b disposed in the first and second rows are used for a small-current circuit, and the small-current circuit pattern 102b is connected to the through holes 103c and 103b. 
Electronic parts (not shown) of various kinds such as a relay and so on are mounted on the parts-mounting area 101b, and these electronic parts are connected to the corresponding through holes 103a to 103c via the circuit patterns 102a and 102b. 
In this related wiring board 101, the terminal connecting areas 101a need to be provided adjacent respectively to the side edge portions thereof to which the connectors 105 are connected, respectively. Furthermore, in order that the L-shaped terminals 104 can be connected respectively to many through holes 103, the L-shaped terminals 104 (104a to 104c) of different heights (h1 to h3) are arranged at the terminal connecting area 101a, and therefore are densely disposed, and therefore a sufficient space for forming the circuit patterns 102 can not be secured at the terminal connecting area 101a. 